15.2 Biomechanics of Walking and Running

Biomechanics of walking and running is all about how our bodies move during these activities. It's like a dance between our bones, muscles, and gravity. Understanding this helps us move more efficiently and avoid injuries.

This topic dives into the differences between walking and running, looking at joint angles, forces, and muscle activity. We'll see how age, gender, and environment affect our gait, and explore why some movements are more energy-efficient than others.

Walking vs Running Gaits

Kinematic Differences

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• Walking and running are two distinct gait patterns that differ in their kinematic characteristics
  • Walking characterized by a double support phase where both feet are in contact with the ground simultaneously
  • Running characterized by a flight phase where both feet are off the ground
• Key kinematic differences between walking and running include:
  • Stride length: Running typically involves longer stride lengths compared to walking
  • Cadence: Running has a higher cadence (steps per minute) than walking
  • Joint angles: Running involves greater flexion at the hip, knee, and ankle joints during the swing phase to facilitate ground clearance
• The transition between walking and running occurs at a critical speed, typically around 2.0 m/s
  • At this speed, the gait pattern shifts to optimize energy efficiency and minimize mechanical stress

Kinetic Differences

• Kinetic differences between walking and running include:
  • Ground reaction forces: Running generally involves higher peak vertical ground reaction forces compared to walking, often exceeding body weight
  • Joint moments: Running requires greater joint moments at the ankle, knee, and hip to support the body and generate propulsion
  • Power generation/absorption: Running involves higher power generation at the ankle and hip joints during push-off, and greater power absorption at the knee joint during the stance phase
• Running places greater mechanical demands on the musculoskeletal system compared to walking
  • Higher forces and joint moments can increase the risk of overuse injuries (stress fractures, tendinopathies)

Gait Biomechanics: Joint Angles, Forces, and Muscles

Joint Angles

• Joint angles of the ankle, knee, and hip play a crucial role in gait biomechanics
  • Ankle joint: Dorsiflexion occurs during the stance phase to control the lowering of the foot, followed by plantarflexion during push-off to generate forward propulsion
  • Knee joint: Flexion occurs during the swing phase to facilitate ground clearance, while extension occurs during the stance phase to support body weight
  • Hip joint: Flexion occurs during the swing phase to advance the limb, while extension occurs during the stance phase to maintain an upright posture
• Joint angles influence stride length, ground clearance, and energy absorption/generation during gait
  • Greater hip and knee flexion during the swing phase allows for longer stride lengths and improved ground clearance
  • Ankle plantarflexion during push-off contributes to forward propulsion and energy generation

Ground Reaction Forces

• Ground reaction forces provide insight into the loading patterns experienced by the lower limbs during gait
  • Vertical force: Represents the upward force exerted by the ground, typically with a double peak pattern during walking and a single peak during running
  • Anterior-posterior force: Represents the braking and propulsive forces, with a braking force occurring during initial contact and a propulsive force during push-off
  • Medial-lateral force: Represents the side-to-side forces, which are generally smaller in magnitude compared to the vertical and anterior-posterior forces
• The magnitude and timing of ground reaction forces can influence joint loading and the risk of overuse injuries
  • Higher peak forces and rapid loading rates may increase the risk of stress fractures and joint degeneration

Muscle Activation Patterns

• Muscle activation patterns are critical for generating the necessary forces and moments to maintain gait stability and propulsion
  • Lower limb muscles, such as the gastrocnemius, soleus, quadriceps, and hamstrings, play key roles in gait
  • Gastrocnemius and soleus: Plantarflexors that contribute to ankle power generation during push-off
  • Quadriceps: Knee extensors that help to support body weight and control knee flexion during the stance phase
  • Hamstrings: Hip extensors and knee flexors that contribute to hip extension during the stance phase and knee flexion during the swing phase
• The coordination and timing of muscle activation are influenced by factors such as gait speed, surface inclination, and individual variations in anatomy and neuromuscular control
  • Faster gait speeds typically involve earlier and greater activation of the ankle plantarflexors and hip extensors to generate more propulsion
  • Uphill walking or running requires greater activation of the hip and knee extensors to overcome the effects of gravity

Energy Efficiency of Gait Patterns

Walking Energy Expenditure

• Walking is generally considered to be more energy-efficient than running at lower speeds
  • Lower metabolic cost per unit distance traveled compared to running at the same speed
• The energy expenditure during walking follows a U-shaped curve, with an optimal speed range where energy cost is minimized
  • Optimal walking speed typically around 1.2-1.4 m/s for adults
  • At speeds slower or faster than the optimal range, energy expenditure increases due to factors such as increased muscle activation and less efficient pendulum-like mechanics

Running Energy Expenditure

• Running has a higher energy expenditure compared to walking
  • Metabolic cost increases linearly with running speed
• The efficiency of running is influenced by factors such as:
  • Stride length: Longer strides can reduce the metabolic cost of running up to a certain point, beyond which energy expenditure increases due to greater vertical oscillation and braking forces
  • Ground contact time: Shorter ground contact times are associated with better running economy, as they minimize the time spent overcoming braking forces
  • Elastic energy storage and return: The tendons and muscles of the lower limbs, particularly the Achilles tendon and calf muscles, can store and return elastic energy during running, contributing to improved efficiency

Self-Selected Gait Patterns

• The concept of the "self-selected" gait pattern suggests that individuals naturally choose a combination of stride length and cadence that minimizes energy expenditure for a given speed
  • This self-optimization process is thought to be influenced by factors such as body size, limb length, and individual biomechanics
• Gait efficiency can be quantified using measures such as:
  • Metabolic cost of transport (COT): The energy required to move a unit distance, expressed as the ratio of metabolic energy expenditure to distance traveled
  • Net mechanical efficiency: The ratio of mechanical work output to metabolic energy input, representing the efficiency of converting metabolic energy into useful mechanical work

Gait Biomechanics: Age, Gender, and Environment

Age-Related Changes

• Age-related changes in gait biomechanics include:
  • Reduction in gait speed and stride length
  • Decreased joint range of motion, particularly at the ankle and hip
  • Alterations in muscle activation patterns, with a shift towards more coactivation of agonist and antagonist muscles
  • Decreased balance control and increased variability in gait parameters
• Older adults often exhibit a more cautious gait pattern
  • Increased double support time and decreased single support time to maintain stability and reduce the risk of falls
  • Decreased step length and increased step width to enhance balance control

Gender Differences

• Gender differences in gait biomechanics are primarily attributed to anatomical and physiological variations
  • Women typically have a wider pelvis relative to their femoral length, leading to greater hip adduction and internal rotation during gait
  • Women also tend to have a greater quadriceps angle (Q-angle), which may contribute to a higher risk of certain overuse injuries (patellofemoral pain syndrome)
• Other gender differences in gait include:
  • Women often display greater ankle eversion and forefoot abduction compared to men
  • Men typically have greater ankle plantarflexion and knee flexion during the stance phase of running

Environmental Factors

• Surface type can significantly influence gait biomechanics and energy expenditure
  • Compliant surfaces (sand, grass) require greater energy expenditure and alterations in gait pattern compared to firm surfaces (concrete, asphalt)
  • Uneven or slippery surfaces can challenge balance control and require adaptations in foot placement and muscle activation
• Incline and decline locomotion place different demands on the musculoskeletal system
  • Uphill gait requires greater hip and knee extensor activation to overcome the effects of gravity and maintain forward progression
  • Downhill gait places greater emphasis on eccentric muscle contractions to control the descent and maintain stability
• External loads, such as backpacks or weighted vests, can alter gait kinematics and kinetics
  • Added load can lead to changes in trunk lean, stride length, and ground reaction forces
  • Asymmetrical loading (carrying a load on one side) can cause lateral trunk lean and asymmetries in gait pattern